The present invention relates generally to the art of compressing a gas. More particularly, the present invention relates to the compression of a refrigerant gas into which a liquid is injected during the compression process. With still more particularity, the present invention relates to the requirement to separate entrained oil from the oil-gas mixture discharged by a compressor in a refrigeration circuit. Finally, the present invention relates to apparatus for centrifugally separating entrained oil from the mixture of compressed refrigerant gas and atomized oil discharged from a screw compressor in a refrigeration circuit as well as to integral apparatus for abating the noise associated therewith.
Compressors are employed in refrigeration circuits to raise the pressure of a refrigerant gas from a suction to a discharge pressure which permits the refrigerant to be used within the circuit to cool a desired medium. Many types of compressors, including rotary screw compressors, are commonly employed to compress the refrigerant gas in a refrigeration circuit.
Two complimentary rotors, a male and a female, are located in the screw compressor housing. The compressor housing has a low pressure end which includes a suction port and a high pressure end which includes a discharge port.
In operation, refrigerant gas at suction pressure enters the low pressure end of the compressor housing and is there enveloped in a pocket formed between the rotating complimentary screw rotors. The volume of the gas pocket decreases and the pocket is circumferentially displaced as the compressor rotors continue to rotate and mesh. The gas within such a pocket is compressed, and therefore heated, by virtue of the decreasing volume in which it is contained, prior to the pocket's opening to the discharge port. The pocket, as it continues to decrease in volume, eventually opens to the discharge port in the high pressure end of the compressor housing and the compressed gas is discharged from the compressor's is working chamber.
Screw compressors used in refrigeration applications will, in the large majority of instances, include an oil injection feature. Oil is injected into the working chamber of the compressor, and therefore into the refrigerant gas being compressed therein for several reasons. First, the injected oil acts to cool the refrigerant gas undergoing compression. As a result, the compressor rotors are themselves cooled allowing for tighter tolerances, in the first instance, between the rotors and between the rotors and the rotor housing which defines the working chamber.
Further, oil injected into the working chamber of a screw compressor acts as a lubricant. One of the two rotors in a screw compressor is normally driven by an external source, such as an electric motor, with the other rotor being driven by virtue of its meshing relationship with the externally driven rotor. The injected oil transmits the drive force and prevents excessive wear between the driving and driven rotors.
Finally, oil injected into the working chamber of a screw compressor acts as a sealant between the meshing rotors and between the rotors and the working chamber in which they are contained in the compressor housing. The oil so injected creates a barrier in the various higher to lower pressure leakage paths which exist within a screw compressor and allows for tighter initial machining tolerances and/or increased efficiency within the compressor.
Oil injected into the working chamber of a screw compressor is atomized and becomes entrained in the refrigerant gas undergoing compression. Such oil, to a great extent, must be removed from the oil-rich mixture discharged from the compressor in order to make the oil available for reinjection into the compressor for the purposes enumerated above. Further, removal of excess injected oil must be accomplished to insure that the performance of the refrigerant gas is not adversely affected within the refrigerant circuit.
Screw compressors have proven to be particularly suited for use in large capacity refrigeration systems with application in 40 to 400-ton systems being common. The size of such compressors and the amount of oil injected thereinto is significant. Injection of one part oil for every five parts of circulated refrigerant by weight coupled with a requirement to remove 90% or more or the injected oil immediately upon discharge of the mixture from the compressor working chamber is typical.
There exist many applications and environments in which the compressor installation is not readily accessible or in which the opening of internal compressor components to the environment is undesirable. In such cases the refrigeration equipment, including the liquid-separation apparatus, is preferably hermetically or semi-hermetically sealed.
Liquid-gas separators have historically comprised large separator receiver combinations which have included, in many instances, baffle schemes to facilitate liquid-gas separation. Such schemes are, as indicated in U.S. Pat. No. 3,917,474 to Heckenkamp et al., neither simple nor inexpensive to fabricate. Further, many such units call for the separator element to be removable in order to allow for its cleaning or replacement.
Exemplary of a second liquid-gas separator for screw compressor applications is that found in U.S. Pat. No. 4,622,048, assigned to the assignee of the present invention and which is incorporated herein by reference. That patent, together with U.S. Pat. Nos. 4,662,190 and 4,762,469 which are likewise assigned to the assignee of the present invention and which are likewise incorporated herein by reference, disclose oil separator portions in a screw compressor assembly having a centrifugal oil separator element which is permeable along its entire length.
While the centrifugal oil separators of the immediately aforementioned patents have proven to be extremely efficient, those designs do not specifically include nor contemplate integral noise attenuation and abatement in general or with respect to certain frequencies in particular. Such noise is characteristic of compressors in general and of screw compressors in particular. Factors in the production of compressor noise including the frequency of the power used to energize the motor (50 cycle versus 60 cycle), the capacity of the compressor, and, in screw compressors, the number of lobes on the male screw rotor which is typically the driven rotor.
The need continues to exist for a highly reliable liquid-gas separator for application in a rotary screw compressor assembly which generally reduces radiated noise and which specifically abates noise at predetermined frequencies while accomplishing the separation of a large majority of the oil from the oil-gas mixture discharged from the compressor's working chamber.